Categories
Productivity Tech

Linux: How To Convert HEIC Files to JPG or PNG

As some of you might know, iPhone has its own picture file format. The HEIC(High-Efficiency Image Container) format. it doesn’t always work when you want to upload it to many websites. There are some websites out there that can convert it for you. It might be okay for some photos that you don’t care about. But for some family photos, you might not want to share them on some random websites.

I found that on Linux, you can simply install a command-line tool called heif-convert. To use it, simply install the libheif-examples command-line. heif-convert just comes with it for free. To install, run the following command:

sudo apt-get install libheif-examples

You can easily convert your HEIC file with the following command:

heif-convert [original-file-name] [file-name-with-jpg-or-png-extension]

For example, if you have a file called IMG_1234.HEIC and want to convert it to IMG_1234.jpg, you can simply run:

heif-convert IMG_1234.HEIC IMG_1234.jpg

Easy, isn’t it? This command can only convert 1 file at a time, which can be annoying when you need to convert multiple files. If you’re lucky, all of the files you drag from the iPhone will have lowercase extension “heic”. You can run this script to convert them:

for file in *.heic; do heif-convert $file ${file/%.heic/.jpg}; done

Sometimes, some files are in lowercase and some come with uppercase. There are many ways to deal with this issue. You can rename all the files to lowercase and then run the above command, you can write a program that reads all the files and then run the heif-convert command.

I took the route to learn about how to do that with a bash script. My script will read all the files that contain “.heic” or “.HEIC” in the filename. Then convert them into jpg format with the heif-convert command.

I created a GitHub repository for any handy command in the future. You can download the heic-converter.sh executable from here. To run it:

./heic-converter.sh

If my note helped, please consider buying me a coffee😁.

Cheers,
Lok

Reference:

https://askubuntu.com/questions/958355/any-app-on-ubuntu-to-open-and-or-convert-heif-pictures-heic-high-efficiency-i

Categories
Tech

How To Copy All The Games From A Micro SD Card To A New One

My 128GB micro SD card is at full capacity and not able to hold all of my Nintendo Switch games anymore. I bought a 400GB micro SD card with a Black Friday deal. Here’s how I clone everything to my new memory card using the dd command. The dd command is a handy tool to copy files bit by bit from one device to another.

There are only 3 steps, but I have a bonus step for you:

  1. Find The Mounted Points
  2. Format the Micro SD Card
  3. Copy The Entire Card
  4. Bonus: Check dd Progress

1. Find The Mounted Points

Mount both memory cards to your computer. Then, run the following command to list all of the mounted drives:

df -h

df is a great command that reports file system disk space usage. The -h flag means to print the output in a human-readable format.

I hid the unrelated stuff, the last 2 rows are what I see from my machine

From the output, I can tell that my 128GB micro SD card is mounted to “/dev/sdc1” in my file system. The new 400GB micro SD card is mounted on “/dev/mmcblk0p1”. The reason why it’s not showing the exact capacity is that I’m using the ext4 filesystem. It reserves 5% of the capacity for important root processes. Here’s an explanation I found on the StackExchange website.

2. Format the Micro SD Card

Since this is a new memory card, we need to format it. There is an easy way to do that with a GUI application called Disks on Linux Mint or any Ubuntu distro. This step is for educational purposes only. Skip this if you don’t want to go through the hassle of the command line.

Nintendo Switch uses FAT32 format. So be it. As we know from step 1, the new SD card is mounted on “/dev/mmcblk0p1”. We need to unmount it first.

sudo umount [path-of-your-new-memory-card]

Remember to change [path-of-your-new-memory-card] to the one you found at your machine in step 1. Below is mine:

sudo umount /dev/mmcblk0p1

Next, we have to create a new partition. I’m assuming you know the path to your memory card from this point. I’m going to use [path-of-your-new-memory-card] instead of my own path.

sudo fdisk [path-of-your-new-memory-card]

You will enter the interface of the fdisk command. It looks like this:

fdisk interface

Type the letter P and hit enter. You will see the information on the partition table of your memory card. Mine looks like this:

Partition table information

Type the letter T and hit enter. You will see the text “No partition is defined yet!”.

Then type the letter N and hit enter. This is the command to create a new partition. Next, type the letter P to select the primary partition type or simply hit enter to select the default.

We only want to create one partition, so type the number 1 or just hit enter to select 1 by default. For the first sector and last sector, also just hit enter to select the default option.

Successfully created 1 new partition on the memory card

Last but not least, we need to change to partition type to FAT32. Type the letter T again and hit enter. Select partition 1, which is the one we just created. Then type the letter b to select “W95 FAT32” format. If you want to explore more options, type the letter L, and hit enter.

After that, type the letter W to save the changes.

All the above are to prepare us for formating. Now we have to actually format the memory card. Use the following command to format the memory card. And your memory card will be usable. 😁

sudo mkfs.vfat [path-of-your-new-memory-card]
Now we have successfully formatted the memory card

3. Copy The Entire Card

This step is simple. Basically, you just run the following command:

sudo dd if=[origin-of-your-file] of=[destination-path] bs=4M status=progress

[origin-of-your-file] is the path that you need to replace with the original micro SD card in your system. [destination-path] is the path of the new card. bs is how many bytes dd command should read and write at a time. The default is 512 bytes. I changed it to 4M, it means 4 megabytes. It’s the same if you just do 4096(without the letter M at the end).

In my case, my actual command would be:

sudo dd if=/dev/sdc1 of=/dev/mmcblk0p1 bs=4M status=progress

Now, just sit back and relax until it finished. The same method can be used to create a bootable Linux image using a micro SD card or USB flash drive. You got the idea.

4. Bonus: Check dd Progress

If you forgot to type in “status=progress” in the dd command like me, you can check the status by opening a new terminal instance. Then type in the following command:

sudo kill -USR1 $(pgrep ^dd)

This will display the progress of the dd command in the original terminal.

It shows 3.2 GB of data is copied after 155 seconds at 20.4 MB/s

If you want to display the progress every n seconds, try the following command:

watch -n[number-of-second] 'sudo kill -USR1 $(pgrep ^dd)'

Replace [number-of-second] with a number. Say you replaced it with 30, then the terminal will display the progress every 30 seconds. See my example below:

watch -n30 'sudo kill -USR1 $(pgrep ^dd)'
This is displayed every 30 seconds in the original window

To stop watching, simply use Ctrl + C in the second terminal. Make sure you do NOT do that in the original terminal that’s running your dd command. Otherwise, you will have to start over again.

Today, we have only touched on the basics of the dd command. Let me know if you have any suggestions.

Categories
Tech

My Journey: Switch From Windows 10 To Linux

Recently I’ve been through a transition from Windows 10 to Linux. Here are a few things that I want to share.

Why Am I Switching?

I have two personal laptops at home. A primary one as a daily driver and an older one is basically sitting there doing nothing. I haven’t directly interacted with the Linux operating system ever since I graduated from college. Since Microsoft has made .Net Core open-sourced and available on basically all operating systems, I’ve always wanted to explore developing .Net applications in Linux(Because it’s cheaper to host web applications on Linux than Windows🀐).

Also for some reason, I’ve been seeing a lot of Linux-related YouTube video recommendations lately, which scratched my itch for learning.

After watching a few videos, I decided to join a few Linux subreddits to learn more. Linux distributions nowadays are very easy to install because they usually come with user-friendly GUIs(Graphics User Interface).

Plus, Linux operating systems are generally more stable and customize-able than Windows. I like the idea that you can make it very personalized and easy to use for your own purpose.

My Concerns

I worried about a few things before switching to Linux. Most people are worried that they cannot play games on Linux. First of all, I have to point out that this is not a big problem anymore. Because many popular games such as Minecraft, Dota 2, Team Fortress 2, Counter-Strike: Global Offensive(and many more) do have Linux versions. I don’t play many games anymore, that’s not my main concern.

I do use Microsoft Office occasionally. I had a formatting issue with LibreOffice before. I’m afraid that I might not be able to get the same experience on Linux. But it turns out that it’s not a big issue anymore.

Other than that, most of my frequently used software, such as Visual Studio Code and Chrome, do have Linux support. Or there are good alternatives. For example, I use an open-sourced remote desktop software called mRemoteNG(highly recommended if you’re on Windows by the way). There are several alternatives on Linux. I ended up with Remmina.

My Manjaro Experience

I started out installing Manjaro on my old laptop. Manjaro is an Arch Linux-based operating system. Arch Linux uses a rolling release model. Instead of having major releases every 6 months or so like other Linux distros(distro means distribution), there are frequent updates released on a weekly or even daily basis. A benefit of that is, you’ll always get the most cutting-edge updates. For example, if there is a security update, you’ll get it right away. Another feature of Arch Linux is that it’s minimalist. You only get the most essential software plus whatever you want to install.

The flip side for Arch Linux is that nothing comes right out of the box and the installation can be confusing for newbies. Manjaro solves this issue. It walks you through a few easy steps and gives you a good-looking user interface.

So I started with Manjaro XFCE(one of the desktop environment choices for Manjaro). Note that on Linux, you can customize many things. The desktop GUI is one of the many things that you can customize.

A screenshot of Manjaro on my Core 2 Duo laptopπŸ˜‚

The XFCE desktop environment is beautiful right out of the box. It’s easy to use and I don’t have to go through the complex Arch Linux installation process. On top of that, you can even install custom software from the AUR(Arch User Repository, a repository maintained by the Arch Linux community). I really liked Manjaro after using it for a week or so.

After a week, my daily driver, which was running Windows 10 had some issues. Then I decided to install Manjaro on it too(YOLO). I’ve been through a few software packages updates. There were some problems here and there and I managed to fix them.

Until one day, I’m not able to boot to the desktop because I delayed an update for a few days, and the latest update broke it. That was the moment I felt tired of keep having to fix issues after the updates. I realized that an Arch-based Linux system is not for me. At least not for daily use. It’s good for people who have more experience with Linux and are willing to spend time fixing issues after each update. I don’t have time for that.

I want a stable environment that works and doesn’t require me to maintain it frequently. So I decided to switch to a relatively more stable distro, Linux Mint.

My Linux Mint Experience

My daily driver machine with Linux Mint

Linux Mint is based on Debian and Ubuntu. It’s relatively stable because Linux Mint comes with Long Term Support and does not require frequent updates. It doesn’t come with the most cutting-edge software like Manjaro. But I’m happy with Linux Mint as my daily driver because I don’t need to worry about breaking it after every update. It just gives me peace of mind.

I kept my older laptop with Manjaro because I still like to explore more of it.

Conclusion

I ended up installing Linux Mint as my daily driver and Manjaro on my older laptop. I’m happy with the result and I’ll keep posting anything I learn.

Categories
Tech

What The Heck Is Docker? Is It Good For Me?

Many people talk about Docker these days. But most of them are hard to understand because people made it sounds too complicated. Today, I want to explain what Docker is in a simple way. Then I’m going to expand into why we should use it, and what are the use cases.

Docker in One Sentence

Docker is a technology that lets you quarantine an application in a tiny version of a Linux virtual machine and runs your applications.

Why You Should Use Docker?

Code Runs The Same in All Environments

Remember the last time when your code works at your local machine but doesn’t work when it’s deployed to the server? By using Docker, this kind of moment will become history. You can put all your applications with the dependency configured in one package(a.k.a. a Docker image). No matter what environment you’re running your application, all the dependents will be created exactly the same. There will be no more “it works at my local but doesn’t work on the server” moments. Isn’t it awesome?

Docker is Really Fast

Imagine you need to setup a virtual machine, how long does it really take? An hour? Thirty minutes? Docker can do that within seconds. Yeah, you heard me rights. Not minutes, but seconds!

For example, if you want to create a Debian Buster environment. Your only need to run two commands. One to download the Debian Docker image to your machine. This part only needs to be done once. Next, run that image with Docker. Just within a few seconds, you can have a fully functional Debian system running. Check out the following video.

Here’s an example of me running an instance of the Debian container from Ubuntu

Did you see how fast it is?

Code Quarantines

That’s right. Your code is quarantined inside a Docker container(I will explain what is a Docker image below). That means you can run an application using Node.js 14.2.0, a different application on 12.12.0, and another one on (if you really want)8.17.0, all in the same machine! The best part is, they won’t affect each other.

Potentially Saves Money

Back in the day, when we need different environments we need to create a new physical server and set up the OS. Now you can install multiple virtual machines with different OS in them. Docker is similar to a virtual machine. But with fewer overheads. Because Docker containers share the same resources, such as the Linux kernel. In the example of running multiple applications with different dependent versions of a framework, you don’t need to buy another virtual machine. Instead, you can put everything in the same virtual machine and run your application via Docker. If you have 10 virtual machines running 10 different environments, you can now do all of that in one machine. Of course, if your applications need to process a lot of data you’ll still need a different machine. But you got the idea.

So, what is Docker really?

Difference between virtual machines and Docker

Just like most computer applications, Docker runs on top of an operating system. We called this “Docker application” Docker. It mediates between the operating system and the tiny version of operating systems that runs on it. The difference between a virtual machine and Docker is that a virtual machine emulates the infrastructure of a computer. For example, CPU, memory, hard disk, etc. When we install an operating system on a virtual machine, it emulates the whole thing.

On the other hand, Docker runs on the Linux operating system. It shares what’s already running on the operating system and shares the resources with the tiny operating systems (Docker containers) that are run on top of it. For example, if your operating system is Ubuntu and you want to run a Debian container. Docker will share the kernel between Ubuntu and the Debian container. Therefore, instead of installing and running the full Debian operating system, you only need a minimal bit of Debian on top of Docker. It doesn’t need to emulate the infrastructure and spin up the whole operating system again. That’s why one of the reasons Docker is so fast.

Docker Image

Now we know that Docker can run a tiny version of a Linux operating system. How does Docker know what should be in each tiny operating system? That is a Docker image. If we just want to run a tiny version of Ubuntu, we’ll still need an image of Ubuntu. That’s a Docker image.

But that’s just the basics. The best part is, you can copy files from the outside to the image and build a new image. You can even host an application and expose specific ports of the tiny Linux. Sounds familiar? Yes, it works just like any virtual machine (but without a graphics interface) and takes much fewer resources from the host operating system.

Docker Container

A Docker container is nothing but a running instance of a Docker image. You can define what goes into a Docker image. For example, an operating system, dependency packages, your application, and so on. Once you run your Docker image, Docker will create an instance of your Docker image as a Docker container.

I have a post about How to Run Docker on Your old Raspberry Pi. That will give you some ideas of how Docker works in action.

If my note helped, please consider buying me a coffee😁.

Cheers,
Lok

Categories
Tech

How to Run Docker on Your Raspberry Pi in 2020

Background

I wanted to learn about Docker. But I don’t want to keep Docker running on my daily drive machine. It happens that I have an old Raspberry Pi 1 Model B+, which I have bought a long time ago, that just sits there doing nothing. So I decided to make it work for me.

The setup

Here’s my plan:

  1. Install Raspberry Pi OS (previously called Raspbian) on my Raspberry Pi
  2. Install Docker
  3. Run Hello World Container
  4. Remove Docker Image

Step 2 – Install Docker

Yes. I’m skipping step 1 here because there is a very detailed setup guide on Raspberry Pi’s website already. I want to focus on the installation of Docker, so I’m not going to repeat it here.

I have followed a few blog posts. Here are the most optimized steps that I found:

0. Login to your Raspberry Pi OS either directly log in through the terminal or remotely login by SSH. Then you should be on this screen:

Note that the top right hand corner says armv6l

1. Update and upgrade your apt-get package tool

sudo apt-get update && sudo apt-get upgrade

2. Download Docker installation script

curl -fsSL https://get.docker.com -o get-docker.sh

3. Execute the installation script

After the download step above. Check that the script is actually downloaded to your machine:

ls
You should see a file called get-docker.sh is downloaded at your current path

Okay, now we can execute the installation script as root user:

sudo sh get-docker.sh

Depending on your internet speed, this step will take a few minutes. Sometimes you would think that your Raspberry Pi is frozen. But give it a good couple of minutes. If it runs successfully, you should see the following on your screen:

4. Add a non-root user to the Docker group

sudo usermod -aG docker [your-user]

This step is to add a user to the Docker user group. If you don’t follow this step, you’ll have to run the docker command as a root user. That means you have to type “sudo” every time you run the docker command. Note that you have to replace [your-user] with your actual user name in the command. For example, my user is pi:

sudo usermod -aG docker pi

The “-a” flag is to add anyone of the group to a supplementary group. In this case, the docker group. We should only use it with the -G option. The “-G” flag is to add a supplementary group. Note that “-G” is case sensitive.

When using the “-G” flag alone, if the user is currently a member of a group that is not listed, the user will be removed from the group. This behavior can be changed via the “-a” option, which appends the user to the current supplementary group list.

5. Check your Docker version

The purpose of this step is not just checking your docker version. It also see if your user is actually successfully added to the docker group. If it works, you shouldn’t need to run the docker command as root. i.e. “sudo”

docker version

If you see a “permission denied” message like I did, do NOT run “sudo chmod 666 /var/run/docker.sock”. This command will give read and write permission to the docker.sock file to every user in the system. As Dave H has mentioned, it will cause a security risk.

Run the following command instead:

sudo chown $USER /var/run/docker.sock

The above command changes the ownership of the docker.sock file to your user. If you run the “docker version” command now, the “permission denied” message should be gone.

Now run the following command:

docker info

and here’s my screenshot:

3. Run Docker Hello World container

If you have a Raspberry Pi 2 or newer, you should be able to run the following command for hello-world without any issue.

docker run hello-world

But for older Raspberry Pi, it doesn’t work anymore. My Raspberry Pi 1 Model B+ for example, doesn’t print the hello-world message like when you run hello-world in other systems. You can check the status of the current docker containers using the following command:

docker ps -a

You’ll see that the hello-world container is excited with code 139. It means the container received a segmentation fault.

After some digging on the internet. I realized that it is not the problem of my installation.

Remember in step 0 when you logged in? The message “armv6l” (the letter after the character “6” is not the number one, it’s the letter “L”) actually indicates the instruction set architecture of this particular model of Raspberry Pi. Although the regular hello-world image works in most cases, somehow the latest version of the hello-world either doesn’t support the armv6 instruction set anymore.

To run any docker image on Raspberry Pi OS, the image have to be built on the same architecture. Here’s the version of Hello World Docker image that works:

docker run --name [myHelloWorld] arm32v5/hello-world

[myHelloWorld] is an arbitrary name that you can give to a container. I’ve named mine as “test”. So mine was:

docker run --name test arm32v5/hello-world

Now you will see a normal Hello World message as the following:

There you go! Now you have successfully get Docker running on your old Raspberry Pi 1 Model B+!

4. Remove Docker Image

To remove a Docker image, you have to first remove the docker container. First, list all the Docker containers:

docker ps -a

You should see a list of Docker containers that have been run. Here’s one way to remove a container. To remove the Hello World container above, for example, you can run:

docker rm test

Now if you run docker ps -a again, the list will be empty.

Then, let’s list the available docker images:

docker image ls

You should see the arm32v5/hello-world image. Let’s remove it:

docker image rm arm32v5/hello-world

I’ve also created a Hello World from my Raspberry Pi. Feel free to try it out.

docker image rm lokarithm/armv6-hello-world

Additional Note

As you may have noticed, you can only run Docker images with armv6 instruction sets(or below) on Raspberry Pi 1 and Pi Zero. To find out whether an image support armv6, you can go to Dock Hub to find the image. For example, I want to run an image of Nginx. I would scroll down to the quick reference section:

Find the supported architecture “arm32v6”

From there, if you see “arm32v6” then click on the link. That means you can pull that image and use it on your Raspberry Pi 1 or Zero.

This is the image we need

In the example of Nginx, you can download the image with the following command:

docker pull arm32v6/nginx:stable-alpine

Note: Usually, if you don’t specify the version of the image, Docker will pull the latest version with a tag called “latest”. But in this case, the latest version is tagged as “stable-alpine” instead. I found the correct version by clicking the tags tab on the page. It should work if you use the same version.

Click on the “Tags” tab to list all the available versions of the image

And then run it:

docker run -p 8080:80 arm32v6/nginx:stable-alpine
You should see messages like the above from your screen

The -p flag simply map port 8080 of the host to port 80 of the image. Now you should be able to browse the default Nginx homepage. If you’re running the command directly from the pi, simply open http://localhost:8080. If you’re like me, who SSH into the pi. You can simply use the same local IP address of your Pi to browse the site. In my case http://192.168.0.58:8080/

It’s that simple. Happy Docker-ing!

Feel free to leave me a message if you have any question.

If my note helped, please consider buying me a coffee😁.

Cheers,
Lok

Side note: I started this post using Putty on Windows 10 to SSH into my Raspberry Pi at the beginning. After a few weeks, I’ve switched to Linux and used Remmina for SSH. So the styling of my screenshots has changed a little.

Categories
Tech

How To Completely Remove Docker From Your Debian Based Linux

This is a simple note to myself of how to remove Docker from Ubuntu or Raspberry Pi OS (previously called Raspbian). Credit goes to Mayur Bhandare on Stack Exchange. I also added some explanation to some of the commands so you will have a better understanding of what they’re doing.

1. Identify which Docker package have you installed
dpkg -l | grep -i docker
For example, I’ve installed docker-ce and docker-ce-cli

The dpkg command is a package management command in Debian. Just like apt-get in Ubuntu, a Linux distro based on Debian. Since Raspberry Pi OS is also a descendant of Debian, this will work just fine. The above command is basically saying, give me a list of packages that contains the word “docker” in them.

2. Remove the packages

For me, I’ve only installed docker-ce and docker-ce-cli. So I will run the following commands.

sudo apt-get purge -y docker-ce docker-ce-cli
sudo apt-get autoremove -y --purge docker-ce docker-ce-cli

If you have more docker packages installed, you can add those packages names to the end of the commands above. For example:

sudo apt-get purge -y docker-engine docker docker.io docker-ce docker-ce-cli
sudo apt-get autoremove -y --purge docker-engine docker docker.io docker-ce 

The “-y” flag here is to answer “yes” to the command prompt when it asks you whether to remove a package. You can choose to remove the “-y” flag. Then you’ll see prompts like the following and you have to manually answer yes or y for every package.

3. Remove all the Docker related files

After that, you might want to remove all the Docker images, containers, volumes, and configurations. This is how:

sudo rm -rf /var/lib/docker /etc/docker
sudo rm /etc/apparmor.d/docker
sudo groupdel docker
sudo rm -rf /var/run/docker.sock

The “-rf ” flag is a combination of the “-r” and “-f” flags. “-r” means recursive. So the rm command can remove all the children folders and files of the target folder recursively. “-f” means force. It will ignore non-existent files, and never prompt before removing them. Be careful when you use these two flags together.

The groupdel command is to delete an existing docker user group.

Bonus: Deactivate Network Interface and Ethernet Bridge

If you want to take one step further, you can deactivate the docker0 network interface and delete the docker0 ethernet bridge. Here’s how(Credit: Thanks to anony for mentioning that!😁):

To disable docker0 network interface:

ifconfig docker0 down

To delete the existing docker0 ethernet bridge:

brctl delbr docker0

Congratulations! You have just completely removed Docker from your system!

If my note helped, please consider buying me a coffee😁.

Cheers,
Lok

Categories
Tech

A Cheatsheet Of Linux File System And Structure

Although I’m not completely new to the Linux operating system, the file system on Linux is still confusing to me. I watched a video about the Linux file/structure system. It’s time to put down some notes and get familiar with them. Let’s go!

  • /bin – binaries:
    • For programs and applications.
  • /sbin – system binaries:
    • For root/admin users only.
  • /boot – contains everything a system needs to boot
    • e.g. boot loader
  • /dev – devices:
    • Everything is a file in Linux. Hardware like a disk, webcam, the keyboard will be stored here, including their drivers.
  • /etc – etcetera:
    • It stores all the system-wide configuration files.
  • /lib – libraries (includes lib, lib32 and lib64)
    • Libraries of applications
  • /mnt and /mnt – mount:
    • For other mounted drives. You’ll typically see /mnt instead of the/mdeia directory. However, most distros nowadays automatically mount devices for you in the media directory.
    • When you mount a drive manually, use the /mnt directory
    • e.g. external hard drive, USB flash drive, network drive
  • /opt – optional:
    • Manually installed software lives here. Some software packages found in the repo can also be found here.
    • You can also put your own software in this directory.
  • /proc – processes:
    • Pseudo files that contain information about system processes and resources.
    • e.g. A directory that contains information on a running process; information of the CPU, etc.
  • /root – home folder of a root user
    • A directory where only a root user has access.
  • /run:
    • A relatively new directory. It is a tempfs file system. It runs in RAM. Anything in this directory will be deleted after rebooting the system. It is used for processes that start early in the boot procedures to store runtime information.
  • /snap:
    • It stores snap packages(mainly used for Ubuntu). Snap packages are self-contained applications that run differently from other applications.
  • /srv – server:
    • It stores server data. Files that will be accessed by external users. e.g. you set up an FTP server. Files can go here, which is separated from the other files for security purposes.
  • /sys – system:
    • A way to interact with the kernel. This is also a temporary directory created every time the system boot up. Similar to the /run directory.
  • /tmp – temporary:
    • Files that temporarily stored for applications. It’s usually empty after you reboot a system.
    • e.g. temporary files of a word processor application.
  • /usr – user application:
    • Applications installed by a user or for a user only. Applications installed in this directory considered non-essential for basic system operation.
    • Under the /usr directory, there are folders such as lib, bin, and sbin.
    • /usr/local contains software installed from the source code.
    • /usr/shared contains larger software.
    • /usr/src contains installed source code such as kernel header files.
    • Different software or distros may treat these folders differently.
  • /var – variable:
    • Files and directories that are expected to grow in size.
    • e.g. /var/crash contains information about files that are crashed; /var/log contains log files of many applications.
  • /home:
    • Each user has its own /home folder.
    • Storage of your personal files and documents.
    • Each user can only access their own /home folder unless they use admin permissions.
    • It has some hidden directories that start with a dot. e.g. .cache, .config. These hidden folders are used by different applications for their settings. You can see them by using the ls -a command in the terminal.
    • You can back up the hidden directories and restore them in a new system. After reinstalling your applications, the settings will be restored.

Credit/Source of information: DorianDotSlash